Catcher for a jet drop recorder

ABSTRACT

There is disclosed an elongated catcher for use with a jet drop recorder which comprises a convex catching face and a recessed drop ingesting blade. The catcher is preferably grounded and positioned in spaced relation to an electrically charged deflection ribbon so as to create a static electrical field between the deflection ribbon and the face of the catcher. Drops of recording fluid which are deflected by the electrical field impact against the backwardly sloping upper portion of the catching face and then flow downwardly along the curving surface of the catching face to the upper surface of the blade. The captured recording fluid, which has preferably spread out into a continuous film, is then ingested into an internal cavity via a series of channels in the upper surface of the blade. To prevent build up of accumulated spray at the top of the catcher there is provided a porous upper surface which connects with a special compartment within the catcher. This compartment is separate from a larger main compartment into which is delivered the ink which is ingested by the blade. Each of these compartments has its own vacuum source for drawing off the liquid accumulated therein. In order to improve downward flow of recording liquid the lower portion of the catching face has a compound radius.

Primary Examiner-Joseph W. Hartary Attorney, Agent, or FirmBiebel, French & Bugg [57] ABSTRACT There is disclosed an elongated catcher for use with 21 United States Patent [191 [111 3,836,914

Duffield ]*Sept. 17, 1974 CATCHER FOR A JET DROP RECORDER jet drop recorder which comprises a convex catching 75] Inventor: Peter L. Dutfield, Kettering, Ohio f and a recessed dmP fl F- The catch [8 preferably grounded and positioned 1n spaced relal Asslgneei Mead p ation, Dayto tion to an electrically charged deflection ribbon so as Ohio to create a static electrical field between the deflection ribbon and the face of the catcher. Drops of re- Nouce' The portlon of the term of thls cording fluid which are deflected by the electrical patent subsequent to Dec. 4, 1990,

has been disclaimed field impact against the backwardly sloping upper portion of the catching face and then flow downwardly [22] File July 20, 1973 along the curving surface of the catching face to the upper surface of the blade. The captured recording [21] Appl' 38l256 fluid, which has preferably spread out into a continu- Relaled US- Application Data ous film, is then ingested into an internal cavity via a [63] Continuation-impart of Ser. No. 317,073, Dec. 20, Series Of Chan l in the upper surface of the blade.

1972, Pat. No. 3,777,307. To prevent build up of accumulated spray at the top of the catcher there is provided a porous upper sur- [52] US. Cl. 346/75, 346/140 face which connects with a special compartment [51] Int. Cl. Gld /18 within the catcher. This compartment is separate from [58] Field of Search 346/75, 140 a larger main compartment into which is delivered the ink which is ingested by the blade. Each of these com- [56] References Cited partments has its own vacuum source for drawing off UNlTED STATES PATENTS the liquid accumulated therein. In order to improve 3,777,307 12/1973 Duffield 346/75 dwnward flow of recordmg l'quld the of the catching face has a compound radius.

2 Claims, 7 Drawing Figures PATENIEUSEPI mu I 38363 14 same 0F CATCHER FOR A .lET DROP RECORDER CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of Ser. No. 317,073 filed Dec. 20, 1972, now U.S. Patent No. 3,777,307, and is related to Ser. No. 317,075 filed Dec. 20, 1972 and Ser. No. 317,076 filed Dec. 20, 1972, now U.S. Patent No. 3,805,273, and to Ser. No. 277,999 filed Aug. 4, 1972, all of which applications are assigned to the assignee hereof.

BACKGROUND OF THE INVENTION This invention relates to a recording head forjet drop recording apparatus, and more particularly to an elongated catcher for use in combination with such a recording head. Typical prior art catchers are shown in Sweet et al., U.S. Pat. No, 3,373,437 and in Rourke U.S. Pat. No. 3,6ll,422. When using such prior art catchers in recording heads of the type shown in Beam et al., U.S. Pat. No. 3,586,907 or, in heads of the type disclosed in Mathis U.S. Pat. No. 3,701,998, serious operating difficulties have been encountered. For instance, if the face of the catcher has a rough porous catching surface of the type disclosed in Sweet et al., then there is a tendency for drops to splatter upon impact thereagainst thereby creating a mist or spray which builds up on electrical components of the head and causes a shorting out thereof. On the other hand, if the droplets are caught by a blade as disclosed in Rourke, then there is a tendency for partially charged drops to strike the tip of the blade thereby splattering and causing ink buildup on the lower surface of the blade.

The capillary catcher which is disclosed in Ser. No. 277,999 offers one solution to the above problems, but catchers made in accordance with that invention are somewhat limited in the volume of ink which they can handle. Thus there has existed a requirement for an improved catcher which can handle relatively high fluid flow rates and which is compatible with a jet array arrangement as shown for instance in the Mathis patent or in arrangements such as those described in Ser. No. 317,075 and Ser. No. 317,076.

SUMMARY OF THE INVENTION This invention provides an improved catcher having a convex drop catching face and a recessed liquid ingesting blade. The catching face is electrically connected to function as a deflection electrode so that drops of recording liquid which have been charged for catching are deflected to impact the catching face against the backwardly sloping upper portion thereof. Thereupon the captured recording liquid flows downwardly along the curving catching face surface for ingestion by the blade. The blade fits tightly against the lower surface of the catcher and ingests the liquid via a series of channels in the blade upper surface. Preferably the portion of the catching face which extends downwardly toward the blade is curved along a compound radius to provide good inward flow while at the same time reducing the tendency of downwardly flowing ink to fly off the catching face. The ink which is ingested by the blade is carried into a chamber within the catcher body and is drawn off by a vacuum source.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded pictorial view of a jet array printer head incorporating the catcher of this invention;

FIG. 2 is a partially cut away top view of the catcher of this invention;

FIG. 3 is a front view of the catcher of FIG. 2;

FIG. 4 is a partially cut away bottom view of the catcher of FIG. 2;

FIG. 5 is an enlarged section view taken along lines 5-5 of FIG. 3;

FIG. 5A is a further enlarged portion of FIG. 5; and

FIG. 6 is a view taken along lines 6-6 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT A. preferred embodiment of the invention as incorporated into a jet drop recording head is illustrated in FIG. 1. The complete head as illustrated in FIG. 1 includes a manifold subassembly 10 which fits into a wobble plate 15. Wobble plate 15 fits into an inner yoke 16 which in turn fits within a main yoke 17. There are also provided a charge ring plate 32, a deflection ribbon 33, and a pair of catchers 18, all of which are fastened to the lower surface of main yoke 17 as hereinafter described.

Manifold subassembly 10 comprises a manifold bar 11, a cover plate 29, an orifice plate holder 12, and an orifice plate 13 which fit together as illustrated in FIG. 1. Thus orifice plate holder 12 fits upwardly into a cavity in the lower surface of manifold bar 11. Orifice plate holder 12 may be secured in place by screws (not shown) and a fluid tight seal is provided between orifice plate holder 12 and manifold bar 11 by an O-ring l4. Orifice plate 13 is preferably soldered in place against the lower surface of orifice plate holder 12. Manifold subassembly 10 is thus an integral unit which may be assembled and flushed clean prior to any association with any of the electrical components ofthe recording head.

As further illustrated in FIG. 1, manifold bar 11 and cover plate 29 are provided with internal passages into which may be inserted an ink supply tube 20, an ink return tube 21, a stimulator 23, and an air tube fitting 24. Stimulator 23 has a probe which reaches downwardly for contact with orifice plate 13. Orifice plate 13 is excited to propagate a series of traveling bending waves as described in detail in Lyon et al, U.S. Pat. No. 3,739,393, and stimulator 23 is rotatably adjustable as described in Houser, U.S. Pat. No. 3,701,476. Air tube fitting 24 is used for applying a flow of purging air to the recording head. A flow of air supplied by a fan or other means (not shown) flows downwardly through air tube fitting 24 and thence into an air cavity 25 in manifold bar 11. The purging air then follows a path around orifice plate 13 to exit the recording head through charge ring apertures 26 in charge ring plate 32. This keeps foreign matter out of the charge ring apertures and also provides a stabilizing effect for the liquid jets. THe jet stabilizing effect, which forms no part of this invention, is described in Sweet U.S. Pat. No. 3,596,275.

Once assembled, manifold subassembly 10 is fitted downwardly into wobble plate 15 and fastened thereto as by screws (not shown). Wobble plate 15, with manifold subassembly attached thereto, if fitted downwardly into inner yoke 16 with an O-ring 27 therebetween. It will be appreciated that wobble plate may be adjusted upwardly or downwardly or tilted within inner yoke 16 for adjustment ofjet filament lengths to meet requirements as discussed in US. Pat. No. 3,739,393. For this purpose there are provided three lifting screws 65 and three hold down screws 66.

Independently of the assembly of manifold subassembly 10, the electrical elements of the recording head may be assembled as a unit by fastening to main yoke 17 as illustrated also in FIG. 1. Charge ring plate 32 is attached directly to the main yoke 17. as are also catchers 18. Charge ring plate 32 is fastened in place by a series of screws. and catchers 18 are secured by means of four cylindrical magnets 34 which are bonded into recesses in the lower surface of main yoke 17. Magnets 34 are common insulated ceramic magnets which are commercially available from many sources. Preferably magnets 34 are made of barium-ferrite ceramic embedded in insulating plastic and are provided with lead-out pole pieces. Catchers 18 are preferably fabricated from a magnetic stainless steel material so that they are firmly grasped by magnets 34.

Lateral adjustment of catchers 18 is provided by set screws 35 and adjusting nuts 36. Each adjusting nut 36 is provided with a small downwardly projecting pin 37 which reaches into a mating recess 62 or 63 (see FIG. 4) in the associated catcher 18. Set screws 35 reach through openings in yoke 17 for threaded engagement with nuts 36. Thus catchers 18 may be adjusted inwardly or outwardly to provide any desired spacing between the catcher faces and the surfaces of deflection ribbon 33.

Deflection ribbon 33 is stretched between a pair of tension blocks 38 which in turn are fastened to main yoke 17 as by screws 39. Tension blocks 38 are provided with set screws 40 so that the tension blocks may be adjusted back and forth in the longitudinal direction. Set screws 40 are initially adjusted to enable easy insertion of deflection ribbon 33 between tension blocks 38. Thereafter deflection ribbon 33 is drawn to a taut condition.

In operation catchers 18 are connected to a common electrical potential source. and deflection ribbon 33 is connected to a source of different electrical potential, so that there are set up a pair of oppositely directed static electrical fields between deflection ribbon 33 and the faces 70 of catchers l8. Droplets of recording liquid which are to be caught are impressed with an electrical charge during the formation thereof and thus are deflected away from ribbon 33 during their transit through the above mentioned electrical fields. This deflection of the charged droplets causes them to impact against one or the other of catcher faces 70.

As shown in FIG. 5 catcher faces 70 have a generally convex configuration comprising a backwardly sloping upper portion 56, a recessed lower portion 57 and a nose or transistion area 61. Drops which are to be caught are deflected to strike the backwardly sloping face area 56 and then flow downwardly along the curve of the catcher face. Preferably the catcher faces 70 are finished sufficiently smooth to avoid drop splattering upon impact but not so smooth as to cause the downwardly flowing recording fluid to bead up into rivulets. Preferably also. the backwardly sloping face portion 56 slopes backwardly at an angle ranging between about 5 and 20 from the vertical. but a slope angle of about 10 has been found to be nearly optimum for effective drop catching.

After the downwardly flowing recording fluid rounds the nose area 61, it flows across the area 57 and toward the blade 51. Blade 51 has a projecting edge 71 which projects out away from the surface area 57, but not as far outwardly as the nose 61. Thus blade 51 intercepts only fluid flowing down the face and does not catch any drops in free flight.

The lower face area 57 preferably has a compound radius as shown in detail in FIG. 5A. Thus there are provided a large radius A and a smaller radius B. The larger radius curve is tangent at its lower end to the smaller radius curve and is tangent at its upper end to the backwardly sloping face portion 56. Nose portion 61 is defined by the larger radius curve.

The purpose of the above mentioned compound radius configuration is to optimize the delivery of ink from catching face 70 to blade 51 while maintaining the shortest practical vertical height for face area 57. The short vertical height is important for decreasing the printing distance (i.e., the distance from orifice plate 13 to the paper therebelow) and improving the printing accuracy. This height consideration produces a requirement for a fairly small radius curve in the region of face area 57. However. another problem arises if the curvature of the face becomes excessive.

When the recording fluid is initially captured by upper face portion, it is traveling at a fairly high velocity. Thus the downwardly flowing film of recording fluid has a rather large inertia which resists any rapid change in direction. Therefore if lower face portion 57 is curved too sharply. the downwardly flowing recording fluid tends to spray off the catching face and miss blade 51 entirely. Accordingly printing distance and ink delivery considerations create conflicting requirements for catching face curvature.

It has been found that as the recording fluid flows down catching face 70 it tends to slow down, so that it may tolerate a continually increasing face curvature without escaping from the surface. This then explains the above mentioned compound radius arrangement. The larger radius A carries the recording fluid around nose 6] and starts it heading inwardly in the general direction toward blade 51. Then after the recording fluid has slowed down somewhat, it is turned sharply around the radius B for delivery to the blade. Obviously a continuously increasing curvature would be somewhat more efficient. but the somewhat simpler double radius configuration has been found to be adequate. In one typical successful embodiment radius A was about 0.6l5cm and radius B was about 0.1 l4cm. For this embodiment the recording fluid was a water base ink, and the initial velocity at impact was about 9 meters per sec.

As shown by FIGS. 2 through 5, a complete catcher 18 comprises a main body 50, the blade 51 and a porous metal insert 52. The main body 50 has a large elongated cavity 53 and a smaller elongated cavity 54. The larger cavity 53 serves as collection chamber for fluid which runs down the catcher face and is ingested by blade 51. Accordingly blade 51 covers the lower surface of main body 50 to close out the cavity 53. Blade 51 fits tightly against main body 50 and protrudes slightly forward of the recessed lower portion of the catcher face. To enable ingestion of fluid by blade 51 there are provided a series of channels 55 as best seen in FIG. 6. A pair of vacuum tubes 41 are connected to communicate with cavity 53 so as to draw off the ink accumulating therein. The vacuum provided by tubes 41 also provides a pressure gradient along channels 55 to cause ingestion of ink by blade 51. In theory only one tube 41 is required, but it has been found that catcher operation is improved by providing vacuum at both ends of cavity 53. As best seen in FIGS. 2 and 4 the catching face 70 of catcher l8 protrudes outwardly from the main body 50 as shown at 60.

The smaller elongated cavity 54 runs substantially the full length of the catching face 70. This cavity communicates with the upper surface of the catcher l8 and is closed out by the porous metal insert 52. There is also a vacuum tube 59 which communicates with cavity 54. In normal operation of a print head of the type shown in FIG. 1 there is created an unavoidable liquid mist or spray in the interelectrode space. This mist, which may be due to drop satellites or other causes, tends to accumulate on the leading edge portions of the upper surface of catchers 18. In addition to the spray accumulation there may also be a build up of liquid on the top of the catcher in the event ofa crooked jet. This build up, if not removed, may bridge across to the charge ring plate and cause electrolytic etching damage. ln accordance with this invention any liquid accumulation at the top of the catcher is drawn through the porous metal 52 into the cavity 54. Thereafter accumulations of liquid in cavity 54 are drawn off by tube 59. There is no interconnection between cavity 54 and cavity 53 because of different vacuum requirements for the two cavities. Typically the catchers operate best with a vacuum in cavity 53 of about 30cm of mecury, while a vacuum in the order of about 20 cm of mecury if satisfactory for cavity 54.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention.

What is claimed is:

1. In a jet drop recording apparatus comprising means for generating a row of parallel drop streams, means for selective charging of drops within said streams, means for establishing an electrical field to deflect those of said drops which are charged as aforesaid, and means for catching the drops so deflected, the improvement wherein said catching means comprises an ingesting blade and a convex catching surface, said surface having a drop catching first portion sloping backwardly away from the paths of said streams and a second portion curving downwardly and inwardly to carry liquid from said first portion to said blade, and said second portion being configured such that the part thereof which is adjacent said blade is curved about a smaller radius than the part adjacent said first portion.

2. The improvement of claim 1 said second portion being curved about 2 radii whereby the part thereof which is adjacent said first portion is tangent thereto and the part thereof which is adjacent said blade is tangent to said other part. 

1. In a jet drop recording apparatus comprising means for generating a row of parallel drop streams, means for selective charging of drops within said streams, means for establishing an electrical field to deflect those of said drops which are charged as aforesaid, and means for catching the drops so deflected, the improvement wherein said catching means comprises an ingesting blade and a convex catching surface, said surface having a drop catching first portion sloping backwardly away from the paths of said streams and a second portion curving downwardly and inwardly to carry liquid from said first portion to said blade, and said second portion being configured such that the part thereof which is adjacent said blade is curved about a smaller radius than the part adjacent said first portion.
 2. The improvement of claim 1 said second portion being curved about 2 radii whereby the part thereof which is adjacent said first portion is tangent thereto and the part thereof which is adjacent said blade is tangent to said other part. 